At 1500 ppm your allready screaming high for most strains ive grown,IMO even staying at 1500 PPM is going to cause problems like burn & lock out so i wouldnt reccomend going higher.
Remember once plants are burnt the damage can never be repaired,also getting a plant unlocked & back on track takes time,the shock slows growth.
Chances are that your allready too high & the plants are not using the majority of the nutes your giving them,i would drop the ppm to below 1,000 but i play it safe.
I have a sativa that can take vast amounts of nutes without burn or lock,ive ran it as high as 1,700 with no damage,i think it could take more but when i dropped nutes to 1,100 growth excellerated & buds were tighter & harder.
Less is more.